/* Copyright (c) 2007 Scott Lembcke
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "chipmunk/chipmunk.h"
#include "ChipmunkDemo.h"

static cpBody* planetBody;

static cpFloat gravityStrength = 5.0e6f;

static void update(cpSpace* space, double dt)
{
    cpSpaceStep(space, dt);
}

static void planetGravityVelocityFunc(cpBody* body, cpVect gravity, cpFloat damping, cpFloat dt)
{
    // Gravitational acceleration is proportional to the inverse square of
    // distance, and directed toward the origin. The central planet is assumed
    // to be massive enough that it affects the satellites but not vice versa.
    cpVect p       = cpBodyGetPosition(body);
    cpFloat sqdist = cpvlengthsq(p);
    cpVect g       = cpvmult(p, -gravityStrength / (sqdist * cpfsqrt(sqdist)));

    cpBodyUpdateVelocity(body, g, damping, dt);
}

static cpVect rand_pos(cpFloat radius)
{
    cpVect v;
    do
    {
        v = cpv(frand() * (640 - 2 * radius) - (320 - radius), frand() * (480 - 2 * radius) - (240 - radius));
    } while (cpvlength(v) < 85.0f);

    return v;
}

static void add_box(cpSpace* space)
{
    const cpFloat size = 10.0f;
    const cpFloat mass = 1.0f;

    cpVect verts[] = {
        cpv(-size, -size),
        cpv(-size, size),
        cpv(size, size),
        cpv(size, -size),
    };

    cpFloat radius = cpvlength(cpv(size, size));
    cpVect pos     = rand_pos(radius);

    cpBody* body = cpSpaceAddBody(space, cpBodyNew(mass, cpMomentForPoly(mass, 4, verts, cpvzero, 0.0f)));
    cpBodySetVelocityUpdateFunc(body, planetGravityVelocityFunc);
    cpBodySetPosition(body, pos);

    // Set the box's velocity to put it into a circular orbit from its
    // starting position.
    cpFloat r = cpvlength(pos);
    cpFloat v = cpfsqrt(gravityStrength / r) / r;
    cpBodySetVelocity(body, cpvmult(cpvperp(pos), v));

    // Set the box's angular velocity to match its orbital period and
    // align its initial angle with its position.
    cpBodySetAngularVelocity(body, v);
    cpBodySetAngle(body, cpfatan2(pos.y, pos.x));

    cpShape* shape = cpSpaceAddShape(space, cpPolyShapeNew(body, 4, verts, cpTransformIdentity, 0.0));
    cpShapeSetElasticity(shape, 0.0f);
    cpShapeSetFriction(shape, 0.7f);
}

static cpSpace* init(void)
{
    // Create a rouge body to control the planet manually.
    cpSpace* space = cpSpaceNew();
    cpSpaceSetIterations(space, 20);

    planetBody = cpSpaceAddBody(space, cpBodyNewKinematic());
    cpBodySetAngularVelocity(planetBody, 0.2f);

    for (int i = 0; i < 30; i++)
    {
        add_box(space);
    }

    cpShape* shape = cpSpaceAddShape(space, cpCircleShapeNew(planetBody, 70.0f, cpvzero));
    cpShapeSetElasticity(shape, 1.0f);
    cpShapeSetFriction(shape, 1.0f);
    cpShapeSetFilter(shape, NOT_GRABBABLE_FILTER);

    return space;
}

static void destroy(cpSpace* space)
{
    ChipmunkDemoFreeSpaceChildren(space);
    cpSpaceFree(space);
}

ChipmunkDemo Planet = {
    "Planet", 1.0 / 60.0, init, update, ChipmunkDemoDefaultDrawImpl, destroy,
};
